This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The ErbB2 receptor is found to be overexpressed and plays an important and early role in the initiation and progression of many types of breast cancer. It was recently found that Erbin, a basolateral PDZ-containing protein, binds to the C-terminus of ErbB2 receptor, through its PDZ domain and plays a critical role in its membrane localization and function. The discovery of the Erbin-ErbB2 interaction, in combination with the recent finding that NHERF binds via its PDZ1 domain to the PDGF receptor tyrosine kinase C-terminus and potentiates receptor autophosphorylation and extracellular signal-regulated kinase activation, raise the intriguing possibility that Erbin potentiates ErbB2 function thought its PDZ interaction.